1. Field
Various embodiments of the present invention relate to an image sensor, and more particularly, to a ramp signal generator with a noise cancelling function and an image sensor including the same.
2. Description of the Related Art
In a typical image sensor with column-parallel structure, since pixel signals having power noise are outputted to a readout circuit, pixel data outputted from the readout circuit includes the power noise.
The power noise coming from pixels may be supply noise, ground noise, both, or any other type of noise.
Since pixel power noise is one of the largest contributors of horizontal noise (HN) in an image sensor, it should be reduced as much as possible.
A switched current ramp signal generator generates a ramp signal by forcing a switching current into a ramp resistor coupled to a ramp ground power supply. In the switched current ramp signal generator, ramp ground bouncing may occur due to line/pad resistance of the ramp ground power supply. The ground power supply of a pixel is used as the ramp ground power supply.
Such ramp ground bouncing of the switched current ramp signal generator serves as a power noise source and has an influence on horizontal noise of the image sensor. Thus, the ramp ground bouncing must be reduced as much as possible.